The magazine sent a sample of DNA from a real crime scene to 17 experienced analysts in an U.S. laboratory. The experts' differing results cast doubts over the technique's reliability.

The sample, from a gang rape, had already been used to convict a man - but only one of the 17 scientists came to the same conclusion. Four said the evidence was inconclusive and 12 said he could be excluded.

Itiel Dror, a University College London scientist who helped set up the investigation, said: 'It is time DNA analysts accept that under certain conditions, subjectivity may affect their work.'

Christine Funk, a defence lawyer in the U.S., said: 'The difference between prison and freedom rests in the hands of the scientist assigned the case.'

That final line should put a shiver through anyone who believes in trial by jury. Hopefully studies like this can put an end to the sort of nonsense we saw from Alan Johnson and Harriet Harman when the pros and cons of removing innocent profiles from the database were being debated.